1. Field of the Invention
The present invention relates to a technique for converting images that have been captured on film into video signals, and in particular, to a technique for converting video signals, which have been converted using a telecine device, to approximate the color tones of a projected film.
2. Description of the Related Art
Images such as movies have up to now been taken using film, this film undergoing the processes of developing and printing and then used to project images on a screen such as in a movie theater. Movies that are shown in movie theaters are also frequently converted to images for television broadcast or video images.
When converting film images to images for television broadcast, a telecine device is used in which light-source light that is irradiated from a prescribed light source is separated into light of the primary color components RGB, the light of each primary color component is irradiated onto the film surface by way of a respective shutter and then captured by a Charge Coupled Device (CCD) camera, the pictures that are successively formed in each frame of a movie film thus being converted to video signals. The use of this telecine device can also solve discrepancies that exist between film images and video signals such as differences in frames per second.
FIG. 1 shows a representative example of the flow of the prior-art process from a developed image that has been captured on film to a broadcast image. Film that has been exposed is progressively developed in a developing process that can be divided into the steps of: camera negative, interpositive, internegative, and release print. The image of the release print is finally shown by means of projection onto a screen, such as in a movie theater. Conversion of images to video signals by a telecine device is normally carried out using film of the interpositive stage.
However, the color purity of a picture gradually deteriorates with each development and printing of film in the course of each stage of the film confirming, and an image that is shown in, for example, a theater has been processed as far as the release print stage and therefore is in a state of relatively degraded color reproducibility. Film in the interpositive stage that is read by a telecine device for converting to video signals has not been subjected to the confirming of the internegative and release print stages and therefore has better color reproducibility than the release print stage. Video signals therefore have better color reproducibility than an image that is shown by film in, for example, a movie theater. The two images differ in terms of color tone and are not equal.
Video signals that have been obtained by the above-described conversion have the characteristic of superior color reproducibility and have a picture quality that differs from an image that is projected from film and shown in, for example, a movie theater.
In recent years, the increase in the size of screens of television sets for home use, the steadily dropping price of plasma displays and liquid crystal projectors, and the increasing number of movies that are broadcast by satellite broadcast or cable TV have all contributed to a growing demand for a movie-viewing experience in the home that approaches the ambience of a movie theater. As described hereinabove, however, video signals that are received in the home have a different picture quality than images shown in, for example, a movie theater, and it has not been possible to reproduce images that are equivalent to images shown in a movie theater.
It is an object of the present invention to provide a method of correcting color purity that can reduce the difference in picture quality that exists between film images and video signals in the prior art and that can reproduce picture quality that approaches that of images shown in a movie theater.
The method of correcting color purity of the present invention for solving the above-described problems is a method of correcting the level of each color component of video signals that have been received as input and outputting the result, wherein the output level of one color component is determined based on and in combination with the input levels of all of the color components.
Because the output level of one color component is determined based on the level of all color components, the color purity falls, and video signals can be outputted that have picture quality that approaches that of film images of the release print stage.
In addition, the method of correcting color purity of the present invention for resolving the above-described problems establishes the relation:       [                            Ero                                      Ego                                      Ebo                      ]    =            [              xe2x80x83            ⁢                                    x1                                y1                                z1                                                x2                                y2                                z2                                                x3                                y3                                z3                              ⁢              xe2x80x83            ]        ⁡          [                                    Eri                                                Egi                                                Ebi                              ]      
where the received video signals are RGB signals; the levels of each color components that have been received as input are Eri, Egi, and Ebi; and the levels of each of the color components that are outputted are Ero, Ego, and Ebo.
The relation between the input signals and the output signals is represented as a determinant, and the correction of each color component can thus be facilitated.
Further, the method of correcting color purity of the present invention for solving the above-described problems stipulates that the value of at least one of y1, z1, x2, z2, x3, and y3 in the determinant shown above is not 0.
The stipulation that the value of at least one of the non-diagonal components in the matrix shown above is not zero means that the output color signals are influenced by other color components of the input color signals and enables a drop in color purity when the colors are mixed.
In addition, in the method of correcting color purity of the present invention for solving the above-described problems, the values of y1, z1, x2, z2, x3, and y3 are stipulated within a range from xe2x88x920.30 to 0.30.
The stipulation that the values of the non-diagonal components of the matrix are within the range from xe2x88x920.30 to 0.30 limits the influence from other color component upon an output color component and thus can prevent a drastic change in picture quality.
Further, in the method of correcting color purity of the present invention for solving the above-described problems, the comparison of the levels Eri, Egi, and Ebi of each of the color components that are received as input is performed by detecting differences between signals; such that y1 and x2 are set to 0 when Eni and Egi are equal, z1 and x3 are set to 0 when En and Ebi are equal, and z2 and y3 are set to 0 when Egi and Ebi are equal.
When the signal levels of each RGB color component of input signals are equal, the input color signal and the display output are achromatic white, black, or gray and color mixing is preferably not performed. Thus, when differences between signals are detected for the purpose of comparing the signal levels of each of the color components and signal levels are found to be equal, gray-scales can be outputted without mixing colors.
Further, in the method of correcting color purity of the present invention for solving the above-described problems, the video signals are obtained by using a telecine device to convert film images of the interpositive stage to telecine images.
Mixing each color component of telecine images to correct color purity enables a reduction of the excess color clarity of film images of the interpositive stage and thus enables an image to be obtained that is equivalent to an image that is experienced in a movie theater.
Further, the method of correcting color purity of the present invention for solving the above-described problems is applied for correction of color purity only when the video signal are telecine image which is detected by telecine image detection device.
In this way, correction of color purity is performed selectively only for telecine images and color correction is not performed for other images, whereby only the excess color clarity of film images of the interpositive stage is reduced and the reduction of the color purity in non-telecine images can be avoided.
In addition, the image display device of the present invention for solving the above-described problems has a means for effecting each of the above-described corrections.
The above and other objects, features, and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings, which illustrate examples of the present invention.